1. Field of Invention
The present invention relates to a gravity separator, primarily of the kind in which a mixture flowing from an oil well, containing water, oil, and gas is separated into discrete, vertically spaced water, oil, and gas layers in a separator vessel for subsequent extraction from the vessel by way of a water outlet, oil outlet, and gas outlet, respectively.
2. Description of the Prior Art
Gravity separators have been known for many decades and have been used within the oil industry in various embodiments of which some are quite complex, including a number of static mixers and cyclones. Examples of known types of gravity separators can be found in e.g. GB 1327991 and WO 99/25454. U.S. Pat. No. 5,080,802 discloses an air flotation separator having an eductor for drawing gas into the incoming fluid. The eductor re-circulates gas collected in the uppermost section of the vessel to the incoming fluid. The separator is provided with a coalescer riser tube positioned substantially in axial alignment with the axis of the vessel, and in order to obtain optimum coalescing high masses of gas, such as a gas to water ratio of about 30% is used. Another gas flotation separator is known from U.S. Pat. No. 5,516,434, and this separator is also provided with a coalescer riser tube with filter medium. A further separator for removing dispersed oil from an oil in water emulsion is disclosed in EP 0 793 987 where gas is dissolved in the inflowing water to form an aerated solution. This solution is introduced to the separator vessel in an assembly of closely spaced matrix plates formed of oleophilic material. The use of coalescer riser tubes with filters or of matrix plates complicates the separator and involves the risk of clogging with a resulting loss of capacity. These prior art designs also require a high degree of maintenance.